The comments in this article suggest that the measurement differences associated with the distinction between assessing exposure to specific campaign messages and assessing exposure to ideas in the public communication environment may become sharper in the context of social/digital media, compared to traditional media. The argument: using social media to deliver specific campaign messages to a large targeted audience is hard, and measurement of exposure will be more demanding than with conventional media sources. In contrast, when the goal is to capture exposure to information in the pubic communication environment, “big data” based content analyses of social media streams may be a valuable approach; still there is much more work to do to establish the validity of these approaches and their usefulness in accounting for behavior.